In two-stroke engines, the pulsating induction flow carries fuel particles during the returning compression stroke which are deposited outside the carburetor either in the upstream air filter or in an elbow pipe located ahead of the carburetor. The fuel collecting there is entrained with the subsequent induction pulses, that is, the pulsating compression strokes operating in the direction of induction. This results in an uncontrolled supply of fuel thereby causing the inducted mixture to be excessively rich. If the fuel entrained by the pulsating return strokes is deposited in the filter itself, the filter will be subject to incrustation and premature contamination thereby affecting its resistance to flow and adversely affecting the induction ratios.
Attempts have already been made to eliminate these disadvantages by extending the induction travel upstream of the carburetor, for example, by inserting an elbow pipe between the carburetor and the air filter. However, the arrangement of such an extension requires an unfavorable mounting position of the filter. Further, the insertion of an additional extension or additional elbow pipe undesirably extends the induction region of the engine. Also, the insertion of an elbow pipe has the disadvantage that the fuel particles in the pulsating induction flow which are still in a gaseous state are deposited in the extension, that is, in the elbow pipe, and change over to a liquid state, so that fuel droplets collect in the intake manifold which are likewise entrained in an uncontrolled manner thereby greatly affecting an optimum carburetor setting.
Moreover, it is known to provide an impact surface on the inside of the filter outer wall upstream of the carburetor on which the returning pulsating induction flow, enriched with fuel particles, impinges. The fuel particles impinging on the impact surface separate in a substantially uncontrolled manner and are usually deposited there as liquid droplets to be subsequently uncontrollably entrained again by the pulsating intake air; or, the fuel particles may be deposited in the air filter as fuel droplets thereby bringing about the above-mentioned disadvantages such as contamination, incrustation, et cetera.